The present invention relates to improvements in precision strain-gage transducers which may be fabricated inexpensively, and, in one particular aspect, to unique high-performance miniature load beams and the like wherein the sensing element is of uniform-thickness flat sheet stock having critical gaged strain-responsive portions defined with great exactness by material removals made in the transverse direction without circular machining, by fine-blanking or the equivalent.
Transducers, in which electrical-resistance strain gages respond to elastic deformations of elements undergoing loading, have long been known in a variety of sizes and forms and for purposes of characterizing such phenomena as force, torque, weight and pressure. From very early stages in the art, it had been established that substantially flat sheet-metal strips which would experience force-induced bending might be gaged directly to yield desired measurement information, as is evidenced by U.S. Pat. Nos. 2,316,203 and 2,321,322. However, perhaps the most common types of constructions, which were evolved to meet needs for general-purpose and high-capacity load cells and beams of exceptional and constant accuracy, came to require that relatively bulky and expensive masses of high-quality metal be shaped into complex configurations. The related set-up operations, tooling, handling, and material-removal machining involved in their manufacture have intensified the labor, material, time and cost associated with intricate shaping and exact dimensioning of such transducers. In addition to the critical deformable sensing portions of the transducers, their load-transmitting end connections have also required accurate machining to insure that forces will always be directed correctly for measurement and that protective enclosures will fit and function properly. For such reasons, transducer designers have favored constructions in which they might rely upon accurate but simple circular-machining of critical portions and coarser slotting or other inexpensive material-removals at portions which are less likely to affect measurements. In particular, the sites at and near gage locations have customarily been machined with a care which is consistent with the need to have the strain gages respond very precisely and repeatably to force-induced surface deformations of underlying material. The latter has been true even in instances where sensing elements of tranducers have been formed substantially flat, the gaged edges and the flat faces both being machined, as in the cases of a load cell element in U.S. Pat. No. 3,222,628 and a force sensing link in U.S. Pat. No. 4,059,012.